linux-kernel - Re: [RFC PATCH] smp: Evaluate local cond

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Message-ID: <207d3b2abb0a9ead709de7b4710e256563b02f3b.camel@surriel.com>
Date: Tue, 03 Dec 2024 12:21:37 -0500
From: Rik van Riel <riel@...riel.com>
To: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: linux-kernel@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>, 
 Ingo Molnar <mingo@...nel.org>, Dave Hansen <dave.hansen@...el.com>, Linus
 Torvalds	 <torvalds@...ux-foundation.org>, Mel Gorman <mgorman@...e.de>,
 x86@...nel.org
Subject: Re: [RFC PATCH] smp: Evaluate local cond_func() before IPI
 side-effects

On Tue, 2024-12-03 at 11:35 -0500, Mathieu Desnoyers wrote:
> In smp_call_function_many_cond(), the local cond_func() is evaluated
> after triggering the remote CPU IPIs.
> 
> If cond_func() depends on loading shared state updated by other CPU's
> IPI handlers func(), then triggering execution of remote CPUs IPI
> before
> evaluating cond_func() may have unexpected consequences.
> 
> One example scenario is evaluating a jiffies delay in cond_func(),
> which
> is updated by func() in the IPI handlers. This situation can prevent
> execution of periodic cleanup code on the local CPU.
> 
> Link: https://lore.kernel.org/lkml/20241202202213.26a79ed6@fangorn/
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
> 

Reviewed-by: Rik van Riel <riel@...riel.com>

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